The present invention concerns photographic copying machines, typically including a light source which transmits exposure light through an original, e.g., a positive or negative film transparency, with an optical system being employed to project the light transmitted through the original onto a photosensitive material, such as photographic print paper, or the like.
When making copies or prints in very-high-quality contexts, and likewise when the originals being copied exhibit special or unusual image content, degree of exposure, coloration, or the like, very high demands are placed upon the knowledge, skill and subjective judgement of the technician who performs the copying or adjusts the photographic copying machine which performs the copying. For example, in the case of photographic copying machines, it is known to scan the transparent original being copied on a pointwise, linewise or zonewise basis, and to derive from such scanning operation information concerning density and/or color which is then used to control the operation of the exposure system of the copying machine, either automatically or with the intermediary of operator participation. The corrective expedients then employed include proper selection of the intensity or duration of the exposure radiation, the use of color filters for establishing a proper spectral composition or balance for the exposure radiation in accordance with subtractive or additive copying procedures, and so forth. However, whatever correction or corrections are established for the intensity and/or spectral balance of the exposure radiation employed, the exposure radiation then actually transmitted through the transparent original is, in general, uniform across the entire surface of the transparent original being copied.
This conventional approach to copying places limits upon the degree of correction of exposure radiation which can be realized, relative for example to the amount of imagedependent information which the image scanners so often used would inherently be capable of affording for later use in exposure correction. For example, if the image on the original is, for whatever reason, markedly overexposed in a certain region, e.g., because of intense light reflection from one bright object within the total subject originally photographed, the point-by-point scanner, or the like, which analyzes degree of original exposure preliminary to printing, could very readily provide information indicating that this zone of the image is excessively overexposed, the remainder of the image not excessively overexposed, and also information defining the location of the points of excessive overexposure. In general, however, even if the scanner were made to supply such information in such form, with conventional printers there is no way in which really to make any full use of this information. At most, the printer will be manually or automatically set to an exposure intensity value, applied across the whole surface of the original, which will represent a course compromise between the fact of localized excessive overexposure and, for example, otherwise proper exposure, with the result that the zones of the image not overexposed must either be somewhat underexposed during printing for the sake of the excessively overexposed zones of the original image, or else be properly exposed during printing but with nothing really done with regard to the zone of excessive original exposure. Similar comments apply to localized problems of color balance, where certain objects, shapes or zones of the image on the original, of complex and generally indefinite configuration, exhibit a color character which is undesirable, e.g., because of the colors of certain objects within the total subject photographed, because of intense light reflection from colored bodies located outside the total subject originally photographed, and so forth.